Calibration of programmable i/o components using a virtual variable external resistor

ABSTRACT

Embodiments provide systems, methods, and integrated circuits having a calibration structure with a calibration component and a measurement structure coupled to the calibration component. The measurement structure is configured to vary a current through the calibration component until a voltage of the calibration component equals an operation voltage. The variable current is a function of at least the operation voltage and a resistance of a resistor external to the measurement structure.

TECHNICAL FIELD

Embodiments relate to the field of electronic circuits. In particular tothe calibration of programmable input/output pad components at anoperating voltage using an external reference resistor.

BACKGROUND

Programmable input/output (I/O) interfaces are programmed to becompatible with various I/O protocols. To accomplish this, theprogrammable I/O pad components (such as resistors and transistors) arecalibrated. Implementations use exact replicas of the programmable I/Opad, an external resistor, and a fixed voltage to measure the effectiveresistance of the pad at the fixed voltage. The external resistor isused because the resistor is sufficiently divorced from the device'spresently-occurring operating conditions, and therefore remains stableenough to provide a reliable reference.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be readily understood by the following detaileddescription in conjunction with the accompanying drawings. Embodimentsare illustrated by way of example and not by way of limitation in thefigures of the accompanying drawings.

FIG. 1 illustrates a measurement structure and an input/outputcalibration structure in accordance with various embodiments;

FIG. 2 illustrates a system having a calibration structure, ameasurement structure, configuration logic, a programmable input/outputpad, and an external resistor according to various embodiments;

FIG. 3 illustrates a more detailed view of a measurement structure and acalibration structure in accordance with various embodiments; and

FIG. 4 illustrates extrapolating programmable input/output padconfiguration parameters and programming input/output pad componentsaccording to various embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which are shownby way of illustration embodiments in which the invention may bepracticed. It is to be understood that other embodiments may be utilizedand structural or logical changes may be made without departing from thescope of the disclosure. Therefore, the following detailed descriptionis not to be taken in a limiting sense, and the scope of embodiments isdefined by the appended claims and their equivalents.

Various operations may be described as multiple discrete operations inturn, in a manner that may be helpful in understanding embodiments;however, the order of description should not be construed to imply thatthese operations are order dependent. Also, embodiments may have feweroperations than described. A description of multiple discrete operationsshould not be construed to imply that all operations are necessary.Also, embodiments may have fewer operations than described. Adescription of multiple discrete operations should not be construed toimply that all operations are necessary.

The terms “coupled” and “connected,” along with their derivatives, maybe used. It should be understood that these terms are not intended assynonyms for each other. Rather, in particular embodiments, “connected”may be used to indicate that two or more elements are in direct physicalor electrical contact with each other. “Coupled” may mean that two ormore elements are in direct physical or electrical contact. However,“coupled” may also mean that two or more elements are not in directcontact with each other, but yet still cooperate or interact with eachother.

For the purposes of the description, a phrase in the form “A/B” means Aor B. For the purposes of the description, a phrase in the form “Aand/or B” means “(A), (B), or (A and B)”. For the purposes of thedescription, a phrase in the form “at least one of A, B, and C” means“(A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C)”. Forthe purposes of the description, a phrase in the form “(A)B” means “(B)or (AB)” that is, A is an optional element.

The description may use the phrases “in an embodiment,” or “inembodiments,” which may each refer to one or more of the same ordifferent embodiments. Furthermore, the terms “comprising,” “including,”“having,” and the like, as used with respect to embodiments, aresynonymous.

In various embodiments, methods, apparatuses, and systems forcalibrating programmable input/output (I/O) pad components using acalibration component—separate from the I/O pad components—a desiredoperational voltage, and an external reference resistance are provided.Known approaches to calibrating programmable I/O pads include using anexternal resistor and a fixed voltage along with an exact replica of theI/O pad being configured. Problems with these approaches arise becausemany I/O pads include transistors, and a transistor's effectiveresistance is substantially non-linear as a function of operatingvoltage. Thus, measuring the effective resistance at a fixed operatingvoltage is not always sufficiently accurate when the desired operatingvoltage of the I/O pad is different from the fixed voltage. Also, usingan entire replica of the I/O pad results in additional complexity andcost.

Embodiments may vary a current through a calibration component modelingan I/O pad component. The current is referenced to an external referenceresistor having a stable resistance, the desired operating voltage, anda variable multiplication factor. Embodiments determine when a voltageacross the calibration component equals the desired operating voltage,and extrapolates at least one I/O pad configuration parameter from atleast the multiplication factor that causes the model component voltageto equal the desired operating voltage. Embodiments may use themultiplication factor to determine an effective resistance across thecalibration component at the desired operating voltage, and use thateffective resistance to extrapolate the I/O pad configurationparameters.

In embodiments, the calibration components may be near or exact replicasof the I/O pad components for which configuration parameters areextrapolated. In other embodiments, some or all of the calibrationcomponents may have different properties from the I/O pad components,but may have sufficient similar operating characteristics as the I/O padcomponents such that configuration parameters can be extrapolated, eventhough an effective resistance across the calibration component at thedesired operating voltage may be different from the effective resistanceacross the I/O pad components at the desired operating voltage.

In embodiments, the calibration components may be subject to the sameoperating conditions as are the programmable I/O pads. That way,determining the effective resistance across calibration components mayprovide useful information as to the appropriate configurationparameters of the programmable I/O pad. Maintaining an externalreference resistor may provide a stable reference resistance such thatthe programmable I/O pad can be accurately configured to have aresistance according to the desired configuration of the programmableI/O pads.

FIG. 1 illustrates a measurement structure and a calibration structurein accordance with various embodiments. Measurement structure 101 maycomprise variable current generator 111, comparison circuit 113, anddesired voltage 115 coupled to both comparison circuit 113 and variablecurrent generator 111. A voltage generator, a digital-to-analogconverter (DAC), or other device may be configured to generate desiredvoltage 115. In embodiments, such devices may be a component withinmeasurement structure 101. Variable current generator 111 may beconfigured to accept voltage 115 and a multiplication factor as inputsand may be configured to be operatively coupled to an external referenceresistor R_(ext). Variable current generator 111 may be configured togenerate a variable current based on the desired operation voltage,R_(ext), and the multiplication factor.

Calibration structure 103 may comprise one or more calibrationcomponents 121 operatively coupled to variable current generator 111 andto comparison circuit 113. In embodiments, calibration component 121 maybe a PMOS transistor, a NMOS transistor, a resistor, or other component.Measurement structure 101 may be configured to vary the variable currentthrough calibration component 121, as it receives incrementally largeror smaller multiplication factor inputs. Comparison circuit may beconfigured to compare the voltage across calibration component 121 todesired operating voltage 115 and to produce a comparison signalindicating which is larger. In this way, measurement structure 103 mayeffectively generate a virtually-variable stable resistor for use tocompare with the effective resistance of calibration component 121 atthe desired operating voltage 115.

FIG. 2 illustrates a system having a calibration structure, ameasurement structure, configuration logic, a programmable input/outputpad, and an external resistor according to various embodiments.Calibration structure 203 may include one or more calibration components221. Measurement structure 201 may include variable current generator211, comparison circuit 213, and desired operating voltage 215 asdescribed above. Configuration logic 205 may be operatively coupled tomeasurement structure 201 and to programmable input/output (I/O) pad207. Configuration logic 205 may be configured to vary themultiplication factor input into variable current generator 211. Inembodiments, the multiplication factor input may be a digital input.Configuration logic 205 may be configured to incrementally increase ordecrease the multiplication factor. In other embodiments, configurationlogic 205 may be configured to vary the multiplication factor in anon-incremental fashion. Configuration logic 205 may be configured toset desired operating voltage 215. In embodiments, configuration logic205 may be configured to output a digital output to a DAC (eitherinternal or external to measurement structure 201) to set operatingvoltage 215.

Variable current generator 211 may be configured to generate a variablecurrent through calibration component 221, based on desired operatingvoltage 215, the multiplication factor, and external reference resistorR_(ext). Comparison circuit 213 may be configured to generate thecomparison signal indicating one or more of whether the voltage acrosscalibration component 221 is greater-than, less-than,greater-than-or-equal-to, or less-than-or-equal to desired operatingvoltage 215.

Configuration logic 205 may be configured to receive a comparison signalfrom comparison circuit 213. Configuration logic 205 may be configuredto determine a multiplication factor that causes a state change in thecomparison signal. Configuration logic 205 may be configured toextrapolate, from this determined multiplication factor, one or moreconfiguration parameters for programming programmable I/O pad 207 and/orI/O pad component 231.

In embodiments, measurement structure 201, calibration structure 203,configuration logic 205, and programmable I/O pad 207 may all beincluded within a single integrated circuit. External reference resistorR_(ext) may be an external resistor, sufficiently shielded from thecurrent operating conditions of calibration structure 203 andprogrammable I/O pad 207.

In embodiments, the layouts of calibration components 221 in calibrationstructure 203 may be carefully controlled during manufacture such thattheir operating characteristics closely match pad component 231 in I/Opad 207. Thus, knowledge of their effective resistances at desiredoperating voltage 215 may be useful to determine the operatingcharacteristics of the I/O pad components at the same voltage. Inembodiments, calibration components may be the same as pad component231. In other embodiments, it may be a scaled version of pad component231. In embodiments, several I/O pads may share the same calibrationcomponents. This may be effective, for example, where several I/O padsare in a bank sharing a single supply voltage. In such cases, the localprocess variations may be small. In embodiments, calibration components221 may be smaller in scale than I/O pad component 231. Theconfiguration logic may then use simple calculations to determine theeffective resistance of I/O pad components 231 from the effectiveresistance of calibration components 221.

FIG. 3 illustrates details of measurement structure 300 and calibrationstructure 350 in accordance with various embodiments. Digital-to-Analogconverter 301 may be configured to accept a digital input “DAC”, alongwith a reference voltage, to produce a desired operation voltageV_(oper). Current generator 303 may be configured to accept V_(oper) asan input. Current generator 303 may also be configured to be operativelycoupled to an external reference resistor R_(ext). Current generator 303may be configured to generate a first current, determined by V_(oper)and R_(ext). Multiplying Current Mirror 305 may be configured to accepta multiplication factor input (“MUL”) and generate a variable currentI_(z) based on the first current and the multiplication factor.

Calibration structure 350 may include one or more calibration componentssuch as PMOS transistors 353 and 355, NMOS transistor 355, and resistor357. In embodiments, more or fewer calibration components may beincluded. A series of pass transistor switches (having with calibrationcontrol points N1, N2, N3, P1, and P2) may be operable to selectivelycouple one of these calibration components to differential amplifier307. MES_P switches may be operable to couple the PMOS transistors tothe negative (“−”) terminal of differential amplifier 307, as well as tocouple voltage VIO to the positive (“+”) terminal of amplifier 307.MES_N switches may be operable to couple NMOS transistor 359 and/orresistor 357 to the positive terminal of amplifier 307, and the negativeterminal of amplifier 307 to ground.

To measure the effective resistance of the PMOS transistors,configuration logic (not shown) may be configured to activate the MES_Pswitches, switch N1, and one of P1 or P2, depending on which PMOStransistor's effective resistance is needed. Enabling switch N1 mayactivate current mirror 361. Current mirror 361 may be configured toduplicate variable current I_(z) through one of PMOS transistors 353 or355 as current I_(p). Current I_(p) through one of PMOS transistors 353or 355 may generate a voltage V_(p) on wire segment P. Amplifier 307 maybe configured to determine an absolute difference between the negativeterminal voltage and the positive terminal voltage. Thus, by selectivelycoupling wire segment P to the negative terminal and the positiveterminal to voltage VIO, amplifier 307 may output a voltage equal to thevoltage across one of PMOS transistors 353 or 355.

Similarly, activating switches MES_N and switch N3 may couple wiresegment N to the positive terminal of amplifier 307 and the negativeterminal to ground. Thus, current I_(z) may be driven through NMOStransistor 359, and generate voltage V_(n) on wire segment N. Amplifier307 may output a voltage equal to the voltage across NMOS transistor359, which may also be equal to voltage V_(n) on wire segment N.Activating switch N2 instead of N3 may couple configuration resistor 357to the positive terminal of amplifier 307 to determine the voltageacross configuration resistor 357.

Comparator 309 may be configured to compare voltage V_(oper) to theoutput of amplifier 307 and to produce a signal indicating whether thevoltage across one of the configuration components is greater than (orless than) V_(oper). In embodiments, differential amplifier 307 mayreliably reproduce the voltages of wire segment N and/or wire segment Pto an input of comparator 309.

Configuration logic (not shown) may be coupled to the output ofcomparator 309 and may be configured to vary multiplication factor MULin an incremental fashion—or other fashion—until the output ofcomparator 309 changes from one state to another. The configurationlogic may be configured to determine configuration parameters for aprogrammable I/O pad (not shown) based on the value of MUL that causesthe output of comparator 309 to change from one state to another. Forexample, the value of the external reference resistance R_(ext) may beknown, as are V_(oper) and the value of MUL that causes the output ofcomparator 309 to change. An effective resistance across one of theconfiguration components may be determined using these values. Inembodiments, the configuration logic may be configured to determine theeffective resistance across one of the configuration components as afunction of R_(ext) and MUL. Configuration parameter values may bedetermined based on this effective resistance. In other embodiments,lookup tables may be used to determine the configuration parametervalues based on the determined value of MUL that causes the effectivevoltage across the configuration component to equal desired operationalvoltage V_(oper), without calculating the effective resistance.

FIG. 4 illustrates extrapolating programmable input/output padconfiguration parameters and programming input/output pad componentsaccording to various embodiments. First a desired operating voltage maybe set block 401. Next, a calibration component may be selected formeasurement block 403. A current through the calibration component maybe varied based on a multiplication factor block 405. Once the voltageacross the calibration component may be determined, block 407, to beequal—or nearly equal—to the desired operational voltage, the currentthat causes the voltages to be equal is determined (such as, forexample, by determining the multiplication factor that causes thevoltages to be equal) and configuration parameters for an I/O pad may beextrapolated block 409. Once extrapolated, one or more I/O padcomponents may be configured using the configuration parameters block411.

Although certain embodiments have been illustrated and described hereinfor purposes of description of the preferred embodiment, it will beappreciated by those of ordinary skill in the art that a wide variety ofalternate and/or equivalent embodiments or implementations calculated toachieve the same purposes may be substituted for the embodiments shownand described without departing from the scope of the disclosure. Thosewith skill in the art will readily appreciate that embodiments of thedisclosure may be implemented in a very wide variety of ways. Thisapplication is intended to cover any adaptations or variations of theembodiments discussed herein. Therefore, it is manifestly intended thatembodiments of the disclosure be limited only by the claims and theequivalents thereof.

1. A system comprising: a calibration structure comprising a calibrationcomponent; and a measurement structure coupled to the calibrationcomponent, the measurement structure configured to vary a variablecurrent through the calibration component until a voltage of thecalibration component equals an operation voltage, the variable currentbeing a function of at least the operation voltage and a resistance of aresistor external to the measurement structure.
 2. The system of claim1, wherein the variable current is further a function of a variablemultiplication factor.
 3. The system of claim 2, further comprising aprogrammable input/output (I/O) pad and configuration logic configuredto extrapolate one or more programmable I/O pad configuration parametersfor the programmable I/O pad from at least a determined particular valueof the variable multiplication factor that causes the calibrationcomponent voltage to equal the operation voltage.
 4. The system of claim3, wherein the measurement structure further comprises a comparatorcoupled to the calibration structure and configured to compare thecurrent operation voltage to the calibration component voltage and toproduce a compare signal indicating which of the two voltages isgreater.
 5. The system of claim 4, wherein the configuration logic isconfigured to vary the multiplication factor and to determine theparticular value of the multiplication factor by reference to a changein the compare signal.
 6. The system of claim 3, wherein theconfiguration logic is configured to program the programmable I/O padusing at least the one or more extrapolated programmable I/O padparameters.
 7. The system of claim 3, wherein the calibration componentis a same type as a I/O pad component of the programmable I/O pad. 8.The system of claim 1, wherein the calibration structure furthercomprises another calibration component, different from the calibrationcomponent, the calibration structure configured to selectively couplethe calibration component and the other calibration component to themeasurement structure.
 9. The system of claim 1, further comprising theexternal resistor.
 10. The system of claim 1, wherein the measurementstructure comprises: a digital-to-analog converter (DAC) configured toaccept a first digital input to produce the operation voltage; a currentgenerator, coupled to the external resistor and to the DAC andconfigured to produce an initial current as a function of the resistanceand the operation voltage; and a current multiplier, coupled to thecurrent generator and to the calibration component, and configured toreceive a multiplication factor as a second digital input and to producethe variable current as a function of the initial current and themultiplication factor.
 11. The system of claim 1, wherein thecalibration component is a transistor or a resistor.
 12. A methodcomprising: setting a desired operating voltage in a measurementstructure, the desired operating voltage equivalent to an operationalvoltage of a programmable input/output (I/O) pad; and varying a currentthrough a calibration component of a calibration structure, differentfrom the programmable I/O pad, until a voltage across the modelcomponent equals the desired operating voltage, the current a functionof an external resistor having a stable resistance and the desiredoperating voltage.
 13. The method of claim 12, wherein the current is afunction of a multiplication factor and wherein the varying the currentcomprises varying the multiplication factor.
 14. The method of claim 13,comprising extrapolating, by configuration logic, at least one I/O padconfiguration parameter from at least the multiplication factor thatcauses the calibration component voltage to equal the desired operatingvoltage.
 15. The method of claim 14, further comprising programming, bythe configuration logic, the programmable I/O pad using at least the oneor more extrapolated programmable I/O pad parameters.
 16. The method ofclaim 12, further comprising receiving, by the measurement structure, afirst digital input indicative of the desired operating voltage, and asecond digital input indicative of the multiplication factor.
 17. Themethod of claim 16, further comprising receiving, by the configurationlogic, a signal indicating whether the voltage across the calibrationcomponent is greater than or less than the desired operating voltage andincrementally increasing, by the configuration logic, the second digitalinput until the signal changes from one state to another.
 18. Anintegrated circuit comprising: a calibration structure comprising one ormore calibration components; and a measurement structure operativelycoupled to the calibration structure, the measurement structureconfigured to vary a variable current through the calibration componentuntil a voltage of the calibration component equals a desired operationvoltage, the variable current being a function of at least the desiredoperation voltage and a resistance of a resistor external to theintegrated circuit.
 19. The integrated circuit of claim 18, wherein thevariable current is a function of a variable multiplication factor. 20.The integrated circuit of claim 19, further comprising configurationlogic configured to extrapolate one or more programmable input/output(I/O) pad configuration parameters from at least a determined particularvalue of the variable multiplication factor that causes the calibrationcomponent voltage to equal the operation voltage.
 21. The integratedcircuit of claim 20, wherein the measurement structure further comprisesa comparator coupled to the calibration structure and configured tocompare the current operation voltage to the calibration componentvoltage and to produce a compare signal indicating which of the twovoltages is greater.
 22. The integrated circuit of claim 21, furthercomprising a differential amplifier coupled between the comparator andthe measurement structure, to reliably reproduce the calibrationcomponent voltage onto an input of the comparator.
 23. The integratedcircuit of claim 21, wherein the configuration logic is configured tovary the multiplication factor and to determine the particular value ofthe multiplication factor by reference to a change in the comparesignal.
 24. The integrated circuit of claim 20, further comprising aprogrammable I/O pad having an I/O pad component, and wherein theconfiguration logic is configured to program the programmable I/O padcomponent using at least the one or more extrapolated programmable I/Opad parameters.
 25. The integrated circuit of claim 20, wherein thecalibration component is a same type as the I/O pad component.
 26. Theintegrated circuit of claim 18, wherein the calibration structurefurther comprises another calibration component, different from thecalibration component, the calibration structure configured toselectively couple the calibration component and the other calibrationcomponent to the measurement structure.